The screens of display apparatuses such as liquid crystal displays are difficult to view under very bright environments. Especially, with respect to display apparatuses that are used outdoors, such as displays for car navigation systems, the screens are likely to get difficult to view due to large variations in surrounding brightness. To always make the screen of a display apparatus comfortable to view, there is known a technique of detecting the illuminance around the display apparatus with an illuminance sensor and adjusting the brightness of the screen according to the detection result of the illuminance sensor.
There are some techniques to adjust the brightness of a screen according to a detection result of an illuminance sensor. For example, one of the techniques is to determine based on detected values obtained from a plurality of illuminance sensors whether to change the brightness of the backlight of a liquid crystal display. This technique does not needlessly change the brightness of the backlight in response to a transient variation in the illuminance. Another technique is to, based on a detected value obtained from an illuminance sensor, gradually dim the backlight when it becomes dark suddenly, and to swiftly brighten the backlight when it becomes bright suddenly. This technique changes the brightness of the backlight so as to fit the adaptation of the human visual system.
Please see, for example, Japanese Unexamined Patent Publications Nos. 2005-121997, 2007-94097, and 07-117559.
By the way, the illuminance around a display apparatus varies according to changes in the surrounding environment of the display apparatus. To make a screen comfortable to view, a display apparatus needs to be adjusted in different ways, depending on how the surrounding environment changes. For example, how to adjust a screen so that people feel comfortable to view the screen is different between the case where the environment suddenly changes from a sunny or cloudy environment to a dark environment like a place in a tunnel or indoor parking area and the case of moving into the shadow of the clouds or buildings from a sunny environment. Therefore, it is desired that a display apparatus is adjusted so that the screen is always comfortable to view under various surrounding conditions.